A video adapter is a device that enables a video display to be interfaced with a data processing system. A primary role of the video adapter is to convert digital image data from the data processing system into electrical signals that may be used by the video display to generate images. The video adapter generally includes a video memory for holding a fixed amount of video data. Unfortunately, the addressable video memory of an adapter is typically quite small. For instance, a video graphics array (VGA) type adapter may have 1 megabyte of video memory or more, but only 64 kilobytes (K) of video memory (i.e., 16 pages of 4K) are visible to the CPU at any one time.
When an image is to be displayed on the video device, the pages of video data for the image are loaded from a linear address space into the video memory of the video adapter. The addressable video memory is part of the physical memory address space of the data processing system. Once the data is loaded into the video memory, the adapter then converts the video data in the video memory into electrical signals that are passed to the video display.